The human body requires at least small amounts of a number of metals in order to maintain health. The diets of many people do not provide sufficient quantities of these metals, and these people benefit from the addition of nutritional supplements to their diets. However, it can be difficult to produce supplements that provide metals in a metabolically available form.
Even for metals which are relatively easy to provide in a metabolically available form, some consumers have an aversion to ingesting chemicals or foods that are perceived as having been artificially processed. Such consumers tend to prefer to eat plant foods which are naturally high in the requisite metals. However, metal-rich edible plants can be difficult to obtain, and metal concentrations tend to be low, so that a large quantity must be eaten in order to obtain sufficient quantities of the metals. These drawbacks become prohibitive when the large number of metals which are beneficial to human health is considered.
An ideal dietary supplement would be an edible plant which contained high concentrations of several beneficial metals, in concentration ratios similar to the ratios considered most beneficial to humans, and contained negligible quantities of toxins. This plant would ideally be easily harvestable in a form which could be eaten fresh or dried, or could be used to form metal-rich tablets or capsules which could be taken as nutritional supplements. Unfortunately, no such naturally-occurring plant is known.
Some attempts have been made to increase the level of selenium present in garlic (Ip, et al., "Potential of Food Modification in Cancer Prevention," Cancer Research (Suppl.) 54:1957s-1959s, April, 1994) and in brussels sprouts (Stoewsand, et al., "Effect of dietary brussels sprouts with increased selenium content on mammary carcinogenesis in the rat," Cancer Letters 45:43-48, 1989), but achievable concentrations were found to be quite small. These two studies, which tested the effect of selenium on mammary carcinogenesis in rats, used dietary fractions of 2% for garlic and 20% for brussels sprouts in order to achieve sufficient selenium levels. These would represent prohibitively large quantities of a single food in a normal human diet.